FLORES R. [2010] NUTRITIONAL COMPARISON OF FROZEN AND NON‐FROZEN FRUITS AND VEGETABLES LITERATURE REVIEW.pdf

Nutritional Comparison of Frozen and Non‐Frozen Fruits and Vegetables:

Literature Review

__________________________________ White Paper

Dr. Gayaneh Kyureghian

402-472-2064 Email: [email protected]

Dr. Jayne Stratton


Dr. Andreia Bianchini


Dr. Julie Albrecht


July 28, 2010

Dr. Rolando A. Flores, Director

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The Food Processing Center University of Nebraska-Lincoln

Achievement of the recommendations made by The Food Processing Center Consultants may be dependent on the occurrence of future events that cannot be assured; thus, changes in future environmental conditions and/or changes in the company’s structure may affect the outcome of the Consultants’ recommendations. While The Food Processing Center believes the information and recommendations are reasonable, no assurance can be given that the projected results will be realized. The information, advice and opinions provided by a University of Nebraska employee represent the best judgment of the employee at that time, but should not be considered legal advice on any local, state, federal or international regulation or statute. We encourage you to contact the applicable regulatory agency and/or qualified attorney to confirm the information presented in this correspondence.

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TABLE OF CONTENTS

ABSTRACT 1

INTRODUCTION 2

The Beginning of a Revolution in Food Preservation 2

LITERATURE SEARCH METHODOLOGY 3

REVIEW 6

Effects of Pre-Freezing Treatments on the Nutritional Value of Fruits and Vegetables and their Phytochemicals

6

Effects of the Freezing Step on the Nutritional Value of Fruits and Vegetables and their Phytochemicals

17

Effects of Frozen Storage (Time and Temperature) on the Nutritional Value of Fruits and Vegetables and their Phytochemicals

18

MACRO DATA 22

Data Aggregation 23

MACRO DATA: TRENDS AND INTERPRETATION 26

Ascorbic Acid 26

B Vitamins 27

Fiber 31

Calcium 36

Carotenoids 38

CONCLUSION 40

REFERENCE 43

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LIST OF FIGURES AND TABLES

Figure 1: The Horizontal Search Process 4

Table 1: Effect of blanching treatment on the vitamin content of a variety of vegetables and leafy greens as reported by several authors

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Table 2: Effect of blanching and freezing on the retention (%) of fiber, phenolic compounds and minerals in different vegetables

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Table 3: Average Ascorbic Acid levels (mg/100g Dry Weight) in a variety of vegetables 28

Table 4: Average data for B vitamins (mg/100g Dry Weight) in a variety of vegetables 30

Table 5: Average Total Fiber levels (g/100g Dry Weight) in a variety of fruits and vegetables 32

Table 6: Average Calcium levels (mg/100g Dry Weight) in a variety of vegetables 37

Table 7: Average Alpha and Beta Carotene levels (mg/100g Fresh Weight) in a variety of vegetables

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1

Nutritional Comparison of Frozen and Non-Frozen Fruits and Vegetables:

Literature Review

ABSTRACT

Fruits and vegetables have long been a nutritious and healthful part of the human diet because

they are low in calories and fat, and are important sources of vitamins, minerals, and fiber. In

addition, fruits are also high in phenolic compounds such as anthocyanins and flavanoids, which

have been correlated with lower risks of chronic diseases. The challenge of the producer has

always been to find ways to preserve food in a high quality state until it reaches the consumer.

Freezing foods has been used for centuries as a preservation method, but it was not until the early

20th century that the technology was developed for mass production and distribution of a variety

of foods. Loss of nutritional value due to the freezing process has been studied extensively in

fruits and vegetables, particularly vitamin C. It is the purpose of this paper to review the existing

food processing, nutrition, and dietary literature for the purposes of preparing this white paper

that conveys, from the body of literature, a comparative analysis of the nutritional contents of

frozen fruits and vegetables to non-frozen produce and products. Traditional search engines

were used to generate an extensive body of literature dating back to 1920’s. Besides compiling

the information available on this subject, this paper also points out gaps still found in the

literature that will guide future research trends based on the current interest denoted by the food

industry.

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INTRODUCTION

The Beginning of a Revolution in Food Preservation

Clarence Birdseye, an American inventor in the early 20th century, was the first to

develop a freezing process that preserved both taste and appearance, in addition to keeping the

product safe from spoilage. In 1922, he founded Birdseye Seafoods from his observations on

how Eskimos in the Arctic preserved fish by quickly freezing them in the environmental

conditions and how the fish tasted fresh when thawed and eaten. Birdseye further developed

freezing technology until 1929, when the first frozen foods were commercially produced

(Archer, 2004).

The concept developed by Birdseye is very simple, where foods are frozen so fast that

large ice crystals are unable to form, hence the name of the technology “quick-frozen”. In the

process of freezing, large ice crystals are formed that can damage cell walls and destroy the

texture and flavor of foods. If these ice structures are unable to form, the frozen food will

maintain its maximum flavor, texture, and color after thawing. Birdseye went on to develop a

double-belt contact freezer that became a US patent and would revolutionize the frozen food

industry. Further development of the frozen food industry happened in the 1940s after the

development of blanching processes which led to a boom of the frozen vegetable industry. After

the achievement of success in stopping enzymatic degradation, the industry of frozen vegetables

gained a strong retail and institutional appeal (Barbosa-Cánovas et al., 2005).

Fruits and vegetables are highly perishable foods subject to rapid deterioration by

microorganisms, enzymes, or oxidation reactions. According to Delgado and Sun (2000),

freezing technology combines the beneficial effects of low temperatures at which

microorganisms cannot grow, chemical reactions are reduced, and cellular metabolic reactions

are delayed; and is a process considered superior to canning or dehydration when the retention of

sensory attributes and nutritional properties are considered (Fennema, 1982). The use of freezing

technologies allows the retention of freshness qualities of fruits and vegetables for long periods,

extending their availability well beyond the normal season of most horticultural crops (Arthey,

1993).

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The process of freezing involves lowering the product temperature generally to -18ºC or

below and maintaining those low temperatures during storage (Kramer, 1979; Fennema, 1973).

Studies done by Guadagni and Kelly (1958) showed that in frozen strawberries the total and

biologically active ascorbic acid remain the same for a year or longer if the food is stored below -

18oC; however, conversion to dehydroascorbic acid (partially active) and 2, 3-diketogulonic acid

(totally inactive) increases with increasing storage temperatures, and nearly complete conversion

occurs in 8 months at -10oC, and less than 2 months at -2oC. These findings were fundamental to

establish -18oC as the upper limit for frozen food storage, and for the use of biologically active

ascorbic acid as an indicator of deterioration in storage. For this reason, much of the literature

on frozen fruits and vegetables include the measurement of ascorbic acid at the different steps of

the process. However, even at such low temperatures, certain enzymatic and non-enzymatic

changes will continue at slower rates, and which limit the storage life of frozen foods (Kramer,

1979).

LITERATURE SEARCH METHODOLOGY

This review of the literature on the nutritional comparison of frozen and non-frozen fruits

and vegetables was conducted in two sequential steps: horizontal and vertical. In the horizontal

step, a “starting point” in the literature was identified which was a review with the closest

objective to the one of the current review. The review used was the one by Rickman et al. (2007)

from the University of California-Davis (UC Davis), entitled “Review: Nutritional Comparison

of Fresh, Frozen and Canned Fruits and Vegetables”, and published in two parts in the Journal of

the Science of Food and Agriculture.

Once the “starting point” was identified, the literature was scanned in retrospect and in

prospect, according to the diagram in Figure 1. In retrospect, the studies in the reference list in

the UC Davis review were scanned and labeled as 1st Generation References. Then the articles

appearing in the reference lists of the 1st Generation References were scanned, and consequently

labeled as 2nd Generation References, and so forth. Occasionally, the same article appeared in

different Generations. These articles were labeled according to their first appearance. A similar

technique was used to scan articles in prospect from the “starting point”. The articles scanned

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were referred to as 1st Generation Citations. The studies that cited articles in 1st Generation

Citations were labeled as 2nd Generation Citations, and so forth.

Figure 1: The Horizontal Search Process

2nd Generation Citations of UC Davis Study

1st Generation Citations of UC Davis Study

UC Davis Study

. . . .

. . . .

Nth Generation Citations of UC Davis Study

1st Generation References in UC Davis

. . . .

2nd Generation References in UC Davis Study

3rd Generation References in UC Davis Study

. . . .

Nth Generation References in UC Davis Study

. . . . . . . .

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The foundation of the vertical search is the source of the publication. The search engines

used to find and retrieve articles for this review were the Web of Science (which includes the

Science Citation Index), PubMed, Google Scholar, University of Nebraska-Lincoln library

resources and interlibrary loans. This process is supposed to endorse the results from the

horizontal search, and possibly reveal articles that were not cited but otherwise satisfy the search

criteria. The vertical search also covered the articles published between the upper time cutoff for

the UC Davis review and the publication year of the UC Davis review.

The search for this review was restricted to the list of the articles that satisfied the

following criteria:

1. Only the articles with explicit relevance to the objective were considered: nutritional

comparison of frozen and non-frozen fruits and vegetables. Therefore, articles that

focused on human health and diet, metabolism of different nutrients, animals, economics,

etc., were excluded from the review.

2. Only peer reviewed articles were considered.

3. Only articles published in English were considered to avoid inconsistencies and

misinterpretations during translations.

4. Studies with qualitative results were excluded. Even though articles with qualitative

results are very insightful, it is hard to combine them with studies with quantitative

results and draw comparisons among them.

5. Research published before 1929 was excluded from the review. The modern freezing

industry began in 1929 with the development of the double belt-contact freezing, which

was adequate for large-scale freezing of fruits and vegetables. Moreover, the blanching

step before freezing has been in use since 1929, which justified the exclusion of the

literature published before 1929 (Archer, 2004).

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REVIEW

Effects of Pre-Freezing Treatments on the Nutritional Value of Fruits and Vegetables and

their Phytochemicals

The freezing process includes pre-freezing treatments, freezing, frozen storage, and

thawing. Even though freezing is regarded as the simplest and most important preservation

process for fruits and vegetables, it is not a perfect process since it is well known that some

nutritional value (vitamins and minerals) may be lost during the freezing process. According to

Fennema (1982), losses of nutrients during freezing can be the result of physical separation

(peeling and trimming prior to freezing, or exudates loss during thawing), leaching (especially

during blanching), thermal (during blanching) or chemical degradation (during storage).

According to Thane and Reddy (1997), some fruits and vegetables require peeling before

processing, such as peaches, tomatoes and carrots. This process may be achieved with the use of

hot water, hot sodium hydroxide solution or mechanical peelers. This process may remove some

of the nutrients with the portions that are separated from the peeled products. Also, by exposing

the flesh/phloem of the fruit/vegetable to the atmosphere, some carotenoid activity may be lost

through oxidation (Thane and Reddy, 1997).

As a pre-freezing process, blanching is used to inactivate enzymes that cause detrimental

changes in color, flavor, and nutritive value during frozen storage (Fennema, 1982); however,

this treatment can also cause loss of such characteristics (Gutschmidt, 1968). According to

Spiess (1984), the loss of water-soluble minerals and vitamins during blanching should also be

minimized by keeping blanching time and temperature at an optimum combination. Almost

every vegetable needs to be blanched and rapidly cooled prior to freezing, and this process is

usually achieved with the use of heat (boiling water, steam or microwave) for a short period of

time. Blanching is usually carried out between 75 and 95ºC for 1 to 10 minutes, depending on the

size of individual vegetable pieces (Holdsworth, 1983). Steam blanching takes longer than the

water method, but helps retain water-soluble nutrients, such as some vitamins and minerals

(Barbosa-Cánovas et al., 2005; Fennema, 1982). After blanching, the product should be rapidly

cooled down to minimize the degradation of heat-labile nutrients (Barbosa-Cánovas et al., 2005).

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In general, since fruits are more sensitive to heat, only a few types are blanched by heating and

the treatment may be achieved by the use of chemical treatments or additives.

Data available in the literature, from 1928 until 1956, concerning the changes in nutrients

and other components, such as minerals, sugars, proteins, carotene, thiamine, riboflavin, niacin,

ascorbic acid, and chlorophyll, during blanching of vegetables was thoroughly reviewed by Lee

(1958). Based on data available at the time, the author mentioned that between water and steam-

blanching, the latter one is the more effective of the two for the conservation of soluble nutrients.

With the introduction of microwave cooking, the field of research for the effect of

blanching on nutrients and quality of frozen fruits and vegetables was revisited to include this

technology, and later on some work with high temperature, short time steam as a blanching

process was also evaluated. Some of the studies on vitamin retention after blanching was

summarized by Lund (1988) and is expanded here to include available information until 2003.

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Table 1: Effect of blanching treatment on the vitamin content of a variety of vegetables and leafy greens as reported by several authors.

Product Nutrient Blanching processa Loss (%) Comments References Ascorbic Acid W, 3 min/93oC 33 W, 6 min/93oC 46 W, 9 min/93oC 58 Riboflavin W, 3 min/93oC 30 W, 6 min/93oC 30 W, 9 min/93oC 50 Thiamin W, 3 min/93oC 16 W, 6 min/93oC 16 W, 9 min/93oC 34 Carotene W, 3 min/93oC 2 W, 6 min/93oC 0

Peas

W, 9 min/93oC 0 Niacin W, 2 min/93oC 32 W, 4 min/93oC 32

Lima beans

W, 6 min/93oC 37

Other temperature-time combinations were done on other vegetables: green beans, lima beans, spinach.

Guerrant et al. (1947)

Ascorbic acid W, 1 min/85oC 10 W, 4 min/85oC 2 W, 8 min/85oC 20 W, 1 min/96oC 0 W, 3 min/96oC 17 W, 5 min/96oC 21 W, 6 min/96oC 25 Thiamine W, 1 min/85oC 1 W, 4 min/85oC 1 W, 8 min/85oC 12 W, 1 min/96oC 0 W, 3 min/96oC 5 W, 5 min/96oC 8

Sweet peas (Immature)

W, 6 min/96oC 0

Loss values calculate on dry solids base. W, 5 min/96oC: value reported here was the average of 5 runs presented by the authors. W, 5 min/96oC: blanched in a commercial blancher; other conditions done in an experimental blancher.

Heberlein et al., (1950)

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W, 1 min/85oC 12 W, 6 min/85oC 18 W, 1 min/96oC 15 W, 3 min/96oC 10 W, 4 min/96oC 14 W, 5 min/96oC 14

Ascorbic acid

W, 8 min/96oC 23 W, 1 min/85oC 3 W, 6 min/85oC 5 W, 1 min/96oC 5 W, 3 min/96oC 12 W, 4 min/96oC 12 W, 5 min/96oC 6

Sweet peas (Nearly mature)

Thiamine

W, 8 min/96oC 14

Peas Vitamin C S 12.3 W 25.8

Holmquist et al. (1954)

Brussels sprouts Vitamin C W, 9 min/88oC 24 S, 11 min/88oC 16 W, 6 min/93oC 16 S, 7 min/93oC 16 W, 5 min/100oC 19 W, 6 min/100oC 20

Dietrich and Neumann (1965)

Brussels sprouts Vitamin C W, 6 min/100oC 43 M, 1 min + W, 4 min/100oC 29 M, 3 min + W, 2 min/100oC 35

Dietrich et al., (1970)

Lima beans Vitamin B6 W, 10 min/100oC 21 S, 10 min/100oC 14

Raab et al. (1973)

Green beans Vitamin C S, 2.5 min 8 mg/100g No initial content reported. IQB 11 mg/100g

Bomben et al. (1973)

Lima beans Vitamin C S, 3.0 min 16 mg/100g IQB 24 mg/100g

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Brussels sprouts Vitamin C S 47 mg/100g IQB 46 mg/100g Peas Vitamin C S 21 mg/100g IQB 18 mg/100g Asparagus Ascorbic acid W, 3.5 or 4.5 min/88oC 35.7 mg/100g S, 3.5 or 4.5 min/88oC 35.3 mg/100g M, 3 or 4 min/1500 W 18.9 mg/100g Green beans Ascorbic acid W, 2 min/88oC 22.5 mg/100g S, 2 min/88oC 23.3 mg/100g M, 4 min/1500 W 13.1 mg/100g Green peas Ascorbic acid W, 2 min/88oC 15.6 mg/100g S, 2 min/88oC 11.0 mg/100g M, 3 min/1500 W 9.3 mg/100g Sweet corn Ascorbic acid W, 2 min/88oC 15.8 mg/100g S, 2 min/88oC 13.6 mg/100g M, 3 min/1500 W 12.9 mg/100g

No initial content reported. Drake et al. (1981)

Mustard greens Ascorbic acid W, 2 min/boiling 55 S, 2.5 min 58 M, 6 min/700 W 55 Green beans Ascorbic acid W, 3 min/boiling 26 S, 4 min 26 M, 4 min/700 W 23 Purple hull peas Ascorbic acid W, 2 min/boiling 29 S, 4 min 11 M, 6 min/700 W 28 Squash Ascorbic acid W, 3 min/boiling 46 S, 2 min 45 M, 6 min/700 W 46

Overall loss for blanching in water 39%, steam 35%, and microwave 38%.

Lane et al. (1985)

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Green beans Ascorbic acid W, 3 min/boiling 13.2 S, 3 min 0 M, 3 min/700 W 9.6

Other combinations of microwave time and conditions were evaluated.

Brewer et al. (1994)

Broccoli Ascorbic acid W, 4 min/boiling 19.5 Brewer et al. (1995) S, 4 min 18.1 M, 4 min/700 W 15.4 Peas Vitamin C W and S, 2 min/95oC 0.0 - 26.7 β-carotene W and S, 2 min/95oC +33.3 - 33.3

Puupponen-Pimiä et al. (2003)

Folic acid W and S, 2 min/95oC 4.3 - 35.0 Carrots Vitamin C W and S, 3 min/97oC 19.0 - 27.9 β-carotene W and S, 3 min/97oC +5.6 - +80.3

Ranges included different varieties for peas and different cuts (cubes or slices) for carrots.

α-carotene W and S, 3 min/97oC +11.3 - +60.0 Cauliflower Vitamin C W and S, 3 min/96oC 16.1 Folic acid W and S, 3 min/96oC 40.2 Cabbage Vitamin C W and S, 3 min/96oC 30.2 Folic acid W and S, 3 min/96oC 61.5

Some nutrients were increased by blanching and freezing (denoted by “+” with the range value)

Potato Vitamin C W and S, 3 min/96oC 26.1 - 26.7 Corn (White Shoepeg)

β-carotene S, 3 min/87.8-93.3oC +189.0 Scott and Eldridge (2005)

Corn (White Shoepeg)

β-carotene S, 3 min/87.8-93.3oC +6.3

aProcess to blanch adequately, generally determined by peroxidase inactivation, or otherwise specified by temperature and time conditions.

W, water; S, steam; IQB, individual quick blanch; M, microwave.

Source: Modified and expanded from Lund (1988).

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From the data on Table 1, the studies done by Heberlein et al., (1950), showed that for

immature sweet peas the best retention was observed in the one minute treatment. However, the

longer the time the sweet peas were maintained at that temperature, the retention of ascorbic acid

was lower in the final product. For nearly mature sweet peas, the authors pointed out that the

retention of ascorbic acid was the same for all the treatments applied from a practical standpoint.

The data obtained for the effect of blanching on thiamine showed that for most of the treatments,

the loss after blanching was less than 10% of the thiamine in the raw peas. Heberlein et al.

(1950) also pointed out that because thiamine does not undergo any oxidative changes during

blanching, it enables the observation of the leaching effect of blanching on this vitamin. Studies

done by Lisiewska and Kmiecik (1991) also showed a loss of 4-10% in the thiamin content and

7-18% in the riboflavin content of broad beans during blanching. In these studies, blanching was

done at 96-98ºC for 2.5-4.0 min, depending upon the degree of seed ripeness, to fully inactivate

targeted enzymes.

In the results provided by Lane et al. (1985), Table 1, except for the steam treatment for

purple hull peas, there was no difference among the blanching processes tested. The biggest loss

in ascorbic acid occurred in mustard greens, which had the largest inherent surface area per unit

weight, and according to the authors, higher losses of ascorbic acid seem to depend on greater

surface-to-mass ratio of the vegetable, rather than on blanching parameters, which also indicate

that losses occur primarily by leaching rather than degradation (Fennema, 1982). When the

overall retention of ascorbic acid by the three blanching processes employed by Lane et al.

(1985) was compared, no difference was observed with retentions varying from 61-65% for

ascorbic acid. The authors attributed the losses to aqueous extraction during the blanching

process, regardless of the amount of water present during the treatment.

When the results obtained by Drake et al. (1981) and Lane et al. (1985), Table 1, are

compared, the greater ascorbic acid content after water and steam blanching showed by Drake et

al. (1981) probably was a result from the shorter blanch time (2 min) and lower water

temperature (88oC) as compared to Lane’s et al. (1985) data (100oC for 3 min); however, because

the initial values of ascorbic acid were not reported by Drake et al. (1981) the actual retention of

the compound cannot be evaluated and direct comparisons between the two sets of data could be

misleading.

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The set of data reported by Brewer et al. (1995) showed no treatment differences existed

in average ascorbic acid retention (15.4 – 19.5%) after the applied treatments (Table 1). Murcia

et al. (2000) also studied the effect of blanching on broccoli (florets and stems). They applied a

water blanching at 92-96oC for 60-150 s and reported a loss in ascorbic acid varying from 50-

51% in the florets and 54-55% in the stems, depending upon the treatment. When data from

Brewer et al. (1995) in broccoli is compared to other vegetables such as mustard greens, green

beans, purple hull peas, and squash studied by Lane et al. (1985) (Table 1); broccoli retained

more ascorbic acid, even when the blanching was done for longer periods of time (4 min in

boiling water as opposed to 2 or 3 min for the other vegetables). When Brewer et al. (1994)

studied the effect of steam, water, and microwave blanching on the retention of ascorbic acid in

green beans the best results were obtained with steam and it was no different than the initial

amount of ascorbic acid quantified in the unblanched samples (Table 1). Wu et al. (1992)

reported a reduction of about 14% on the dried weight basis (DWB), or 17%, on wet weight

basis (WWB), of ascorbic acid in green beans during blanching for 3 min in boiling water; while

broccoli was reported to lose about 21% (DWB) or 40% (WWB).

The results reported by Puupponen-Pimiä et al. (2003) were for vegetables that were

water and steam blanched, followed by quickly freezing at -40oC (Table 1). The authors

considered that the freezing step did not affect the nutritional value of the vegetables and all the

differences observed between the raw and frozen product were attributed to the blanching step.

More discussion on the effects of the freezing step will follow. Therefore, according to the

authors, significant losses of vitamins were observed in many of the treatments applied. Vitamin

C losses were strongly plant and species dependent, with the highest losses around 30%. As

much as a half of folic acid was lost during blanching as a result of its solubility and reactivity.

De Souza and Eitenmiller (1986) also studied the effect of blanching on the folate content of

spinach and broccoli. After treatment, they reported losses of 83% and 42% for water and steam

blanching for spinach and 60% and 9% for water and steam blanching of broccoli. For some

vegetables, like carrots and some species of peas, Puupponen-Pimiä et al. (2003) reported the

increase in concentration of carotenoids right after blanching and freezing. Van den Berg et al.

(2000) have discussed both the negative (loss due to oxidation) and positive (increased

bioavailability) impact of food processing on carotenoids, which may explain the higher

carotenoid content in blanched vegetables reported by Puupponen-Pimiä et al. (2003).

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Scott and Eldridge (2005) reported significant increases in the level of β-carotene in corn,

especially on the White Shoepeg variety, after blanching and freezing, as showed in Table 1. The

authors compared the β-carotene contents of fresh and frozen corn on a fresh weight basis, and

attributed the increases observed to a possible dehydration of the kernels as the result from water

weight losses during steam blanching and freezing.

In general, the data presented in Table 1 shows that for water blanching, the loss of

water-soluble vitamins increases with contact time, and fat-soluble vitamins are relatively

unaffected. Steam blanching, in general, resulted in greater retention of water-soluble vitamins.

The IQB process seems to be better than steam for blanching; however retention data were not

available for this process, which makes a broader comparison between this method and nutrient

retention obtained with other studies using steam blanching difficult.

Drake and Carmichael (1986) compared the effect of water blanching with a high

temperature, short time (HTST) steam blanching on the amount of ascorbic acid in different

vegetables after treatment. After blanching, the vegetables were frozen and stored for 90 days at

-23oC. They found that snap peas treated with water (82oC 3 min) and steam (45 psi 35-55 sec)

did not show differences in their ascorbic acid content, except for the treatment at 45 psi for 35

sec, which resulted in less destruction of ascorbic acid. Sweet peas were treated with water at

88oC for 2 min and steam at 15-20 psi for 35-45 sec, and none of the treatments differed in the

amount of ascorbic acid after blanching. For lima beans the treatments applied were water at

88oC for 2 min and steam at 20-40 psi for 20-60 sec, and the amount of ascorbic acid decreased

as the time of the HTST increased. Lima beans blanched at 20 psi for 60 sec showed 23% less

ascorbic acid than the water-blanched product. When carrots were evaluated, the treatments were

water at 88oC for 2 min and steam at 45-60 psi for 30-60 sec, and the results showed that

ascorbic acids were significantly greater for the HTST-blanched carrots at 45 psi for 40 sec or 60

psi for 30 sec, when compared to the water-blanched carrots.

The effect of blanching conditions on the amount of fiber, minerals and phenolic

compounds was also studied by Puupponen-Pimiä et al. (2003). The data reported by these

authors were for vegetables that were water and steam blanched, followed by quickly freezing at

-40oC. For this study, the authors considered that any differences observed in the final product

regarding the nutrients and compounds evaluated were a result of the blanching step. From the

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retention data in Table 2 and according to Puupponen-Pimiä et al. (2003), dietary fiber

components were rather stable during blanching, and they were either not affected or increased.

The authors suggested that the observed increase in fiber was a result of the washing out of

soluble components and small molecules leading to the concentration of fiber components in the

processed material. Another explanation would be the mechanical disruption of cells during

processing that might have resulted in better extraction of fiber components. Pentosans and

pectins behaved much in the same way as dietary fiber.

Among minerals, potassium contents were often decreased during blanching, especially

in spinach. The authors indicate that the behavior of minerals during blanching is related to their

solubility. Potassium, the most abundant mineral in vegetables, is extremely mobile and is easily

lost by leaching during blanching because of its high solubility in water. Calcium and

magnesium are generally bound to the plant tissue are not readily lost by leaching, and

sometimes can even be taken up by vegetables during blanching from the processing water in

areas with hard water. In general, the amount of total phenolics decreased during blanching by

20-30%.

Ninfali and Bacchiocca (2003) studied the effect blanching and freezing on the amount of

polyphenols and antioxidant capacity of vegetables. The authors reported that the amount of

phenols and oxygen radical absorbance capacity (ORAC) values in frozen beet greens were

about 30 and 12%, respectively, of those observed in the fresh vegetable. The loss was related to

the need of a drastic processing conditions imposed by the texture of the vegetable, and it was

suggested that the use of younger beet greens could allow the blanching time to be reduced, thus

saving the antioxidant capacity. Frozen broccoli, however, did not show differences in the

ORAC value when compared with the fresh vegetable, indicating that the blanching method was

mild enough to preserve the antioxidant capacity of the product.

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Table 2: Effect of blanching and freezing on the retention (%) of fiber, phenolics compounds and minerals in different vegetables.

Sample Soluble fiber

Insoluble fiber

Total dietary fiber

Pentosans Pectins Total Phenolics

Ca

Mg

K

P

Na

Cu

Mn

Fe

Zn

Peasa 149 106 107 108 84 79 114 97 80 94 130 83 102 102 93

Carrotsb 115 125 120 134 130 92 119 110 98 106 88 92 146 101 96

Cauliflower 113 109 110 98 100 87 100 89 84 87 87 115 75 94 70

Cabbage 154 118 125 125 143 126 - - - - - - - - -

Spinach 88 112 108 133 123 - 109 73 64 87 60 100 76 105 112

Potato 83 111 97 116 190 71 75 91 84 90 ND 92 95 97 176 aData included different species of peas; bData included different cuts (cubes and slices) -, not determined; ND, below detection limit.

Source: Puupponen-Pimiä et al. (2003).

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Effects of the Freezing Step on the Nutritional Value of Fruits and Vegetables and their

Phytochemicals

According to Selman (1992), the process of freezing itself does not alter the nutritive

value of the product being frozen. It is during the preparative steps prior to freezing, particularly

blanching as discussed earlier in this paper, and during subsequent frozen storage that losses of

more labile vitamins occur. Fennema (1982) lists a series of more than 10 papers that indicate

that the freezing step generally has no significant effect on the vitamin contents of vegetables

and fruits. Research done by Drake et al. (1981) on freezing using a Lewis individual quick

freezing (IQF) tunnel and blast freezer also did not show differences in the ascorbic acid content

of vegetables (asparagus, green beans, green peas, and sweet corn). Lisiewska and Kmiecik

(1991) also reported no effect of freezing on the contents of thiamin and riboflavin of broad bean

seeds. And this concept could also be extended to other components of fruits and vegetables and

follows in the discussion presented here.

According to Thane and Reddy (1997), the amount of carotenoids is also not affected by

freezing, particularly rapid freezing. Deteriorative process occurs, although at a very low rate,

during storage. This is desirable, of course, because of the high value placed on carotenoids as

nutrients.

The effect of freezing on the total flavonoids and anthocyanin contents of red raspberries

was studied by Mullen et al. (2002). In their study, raspberries were frozen within 3 hours of

picking at -30oC, without any additional treatment. The total flavonol content of fresh raspberries

was not significantly different than in the frozen product (22.3 – 27.0 nmoles/g fresh weight). Six

major anthocyanins were also analyzed separately and no significant differences either in the

levels of the individual anthocyanins or in the overall anthocyanin content of the fresh and frozen

raspberries were reported. De Ancos et al. (2000) showed that the freezing process had little

effect on the ellagic acid, total phenol, vitamin C content, and antioxidant capacity on Spanish

raspberries.

Even though most of the scientific reports indicate that the freezing step does not greatly

affect the nutritional value and composition of fruits and vegetables, some do and should not be

neglected. Cano et al. (1993) studied the effect of freezing on four Spanish kiwi fruit cultivars. In

18

their study, the fruits were washed, peeled and sliced (6-8 mm) and frozen in an air-blast freezer

at -40oC, without any previous treatment. In general, the total acidity of the kiwi fruit slices

decreased slightly during the freezing process, with one of the varieties tested (Monty) losing

20% when compared to the raw fruit total acidity. The amount of ascorbic acid was decreased by

10-25% depending on the cultivar considered, with only one variety (Bruno) not showing any

reductions due to freezing. However, the soluble solids of frozen kiwi fruit slices did not change

significantly during freezing. The amount of total and individual sugars also did not change

much, except for one variety (Hayward) where it increased, and the authors related that to the

different cell wall structure and higher moisture content of this variety.

Effects of Frozen Storage (Time and Temperature) on the Nutritional Value of Fruits and

Vegetables and their Phytochemicals

An extensive body of literature is available on the effects of time and temperature storage

on the nutritional value of fruits and vegetables. In general, foods are known to remain well

preserved at -18oC, but storage at higher temperatures and/or for long periods of time can cause

vitamin losses and marked effects on color and flavor, which results in lower quality at the retail

level. Vitamin loss during frozen storage also depends on the product, the type of packaging and

the use of additives or sugar (Derse and Teply, 1958; Fennema, 1982).

According to a review done by Fennema (1982), losses of vitamins C, B1 and B2 during

frozen storage are usually considerably less in blanched vegetables than in unblanched, with

some data indicating that blanched losses are only 25 to 50% as much vitamin C when compared

to unblanched products. However, the author highlights that it is not necessarily true that losses

incurred by blanching are compensated for by the reduction in losses that would otherwise occur

during freezing storage. Such compensation is, according to Fennema (1982), especially unlikely

when products are stored for only a short time at -18oC or lower. Data on the effect of

subfreezing temperatures on the rate of vitamin C degradation in vegetables indicates that a 10oC

rise in temperature, within the range of -18 to -7oC, accelerates vitamin C degradation by a factor

of 6 to 20 times, while in fruits (peaches, boysenberries, and strawberries), it is increased by a

factor of 30 to 70 times (Fennema, 1982).

19

Lee and Coates (1999) related the loss of vitamin C in fresh squeezed orange juice that

had been stored frozen to oxidative enzyme reactions. During processing and storage, ascorbic

acid can be enzymatically oxidized to dehydroascorbic acid, which has equal antiscorbutic

activity; however it is not stable and is hydrolysed to 2,3-diketogulonic acid and further

breakdown products (Selman, 1992). Eheart (1970) studied the effect of storage at -15oC for up

to 5 months on the composition of frozen broccoli. They found that after 5 months of storage,

there were significant losses of reduced ascorbic acid (31%) and total ascorbic acid; while the

amount of dehydroascorbic acid increased. Total acids also increased, while pH decreased during

storage. Similar results were reported by Martin et al. (1960) when evaluating the factors

affecting the ascorbic acid in broccoli during frozen storage. In their studies, broccoli was

maintained at -18oC for 25 weeks and during this period, an increase in dehydroascorbic acid

was observed between weeks 15 and 17 of storage. They also reported an increase in the

diketogulonic content of the product between weeks 2 and 13, along with a gradual decrease in

reduced ascorbic acid with the storage time. As both dehydroascorbic acid and reduced ascorbic

acid are biologically active, the decrease in reduced ascorbic acid is partially compensated for by

the increase in dehydroascorbic acid, denoting the importance of measuring both forms during

processing and storage studies (Martin et al., 1960).

During storage at -20oC, Wu et al. (1992) reported that even after 16 weeks the ascorbic

acid content of green beans and broccoli had not changed when compared to the levels

immediately after freezing. However, after 30 months at -22oC, the vitamin C content of frozen

cauliflower was reduced by 62.2%. The 50% loss in vitamin C in the frozen cauliflower took

place at approximately 26 months of storage, while the 25% loss occurred at about 13 months

(Aparicio-Cuesta and Garcia-Moreno, 1988). Favell (1998) also studied the losses of ascorbic

acid during frozen storage of vegetables and found that after 12 months of storage at -20oC, the

decrease in the ascorbic acid content of peas and broccoli was less than 10%, in green beans was

less than 20%, and in spinach it was about 30%.

The effect of frozen storage has also been studied in fruits (strawberries, raspberries and

kiwi), and fruit processed products (orange juice). When Sahari et al. (2004) evaluated the effect

of low temperature on ascorbic acid, they reported that strawberries stored at -12, -18, and -24oC

showed significant decreases of 64.5%, 10.7%, and 8.9%, respectively, in the ascorbic acid

20

content after 90 days of storage, with major losses occurring during the first 15 days of storage at

-12oC (31.4%). Frozen storage of raspberries for one year at -20oC showed a continuous

decrease in vitamin C with time, in all four cultivars studied, with loss of 33-55% at the end of

the long-term frozen storage (De Ancos et al., 2000). The effect of frozen storage (1 year at -

18oC) on the ascorbic acid content of four Spanish kiwi cultivars was studied, and all cultivars

showed some loss of this nutrient with storage; with the cultivar Bruno, showing the most

significant decrease (37%) (Cano et al., 1993). Lee and Coates (1999) showed that after 24

months of storage at -23oC, frozen, fresh-squeezed, and unpasteurized orange juice had its

vitamin C content reduced from an initial value of 40.6 mg/100 mL to 32.8 mg/ 100 mL for a

loss of 19.2% over the storage period. According to the authors, the estimated shelf-life of the

product to meet the claimed levels of vitamin C on the label would be about 22 months.

The effects of frozen storage on the levels of vitamins and minerals in green beans, peas,

strawberries and orange juice concentrate were studied by Derse and Teply (1958). They

reported that after 12 months of storage at -18oC, only green beans showed appreciable losses in

ascorbic acid (50%), with results possibly indicating a variable decrease in folic acid,

pantothenic acid, riboflavin, vitamin B6 and in some of the minerals evaluated. According to

Selman (1992), during storage at -18oC over one year, the loss in the thiamin content of

vegetables like asparagus, broccoli, green beans and peas was about 20%. Spinach and

cauliflower seem to be more sensitive with losses up to 50%.

De Souza and Eitenmiller (1986) studied the effect of frozen storage on the amount of

total folate activity (TFA) in spinach and broccoli, and reported a 72% retention of TFA in

spinach after 3 months of storage and 83% in broccoli after 8 months of storage at -32.2oC, when

compared to the TFA in the products after water-blanching and just before freezing. Puupponen-

Pimiä et al. (2003) mentioned the importance of enzymatic inactivation to prevent degradation of

folate, even when vegetables are stored frozen. In their studies, freezer storage (-20oC for 18

months) did not affect the amount of folic acid in peas, cauliflower, broccoli, cabbage and

spinach.

When studying the effect of frozen storage on the levels of carotenoids in sliced carrots,

Crivelli and Polesello (1973) reported a 60% loss after 12 months at -20oC. Puupponen-Pimiä et

al. (2003) showed that during frozen storage of peas (-20oC for 18 months), 17% of the β-

21

carotene content was lost; while in carrots the loss varied from 27 to 75% depending upon how

the products had been processed (cubes or slices) and their harvest year (1997 or 1998). The

effect of freezing and storage on the carotenoid composition of papaya slices was studied by

Cano et al. (1996). In their studies slices of papaya fruit were vacuum-packed and frozen in an

air-blast freezer at -40oC, without any previous treatment. The frozen product was stored at -

18oC for 12 months and the results obtained showed that the carotenoid content of frozen papaya

slices was significantly decreased. The reduction in carotenes was higher in female frozen slices

(65%) than in hermaphrodite ones (14%), and the differences were attributed to different

enzymatic behaviors shown by female and hermaphrodite frozen slices during storage.

When the effects of frozen storage (-20oC for 4 months) on the amount of total

anthocyanins in cherries was studied, Polesello and Bonzini (1977) observed a decrease varying

from 34 to 73%, depending upon the cultivar and it was not related to their initial concentration.

Chaovanalikit and Wrolstad (2004) also studied the effect of frozen storage in the anthocyanin

content of cherries, and they reported that storage at -23oC for 6 months caused up to 87%

degradation, with an increased amount of polymeric color (from 12.5 in fresh cherries to 61%

after frozen storage); while storage at -70oC resulted in much greater anthocyanin stability with

88% remaining after 6 months. However, De Ancos et al. (2000) did not observe any change in

the monomeric anthocyanin content of raspberries stored frozen for up to 1 year at -20oC. Similar

results were also reported by Hager et al. (2008) for monomeric anthocyanin and polymeric

color in individually quick frozen blackberries stored for 6 months at -20oC.

In cherries, the amount of total phenolics was evaluated throughout frozen storage for 6

months at -23oC and -70oC by Chaovanalikit and Wrolstad (2004), and they reported 25%

degradation after 3 months and 50% after 6 months at the higher temperature, with minimal

changes at the lower temperature. The levels of ellagic acid, a polyphenol antioxidant found in

numerous fruits and vegetables during frozen storage of raspberries were studied by De Ancos et

al. (2000). When the fruits were maintained at -20oC for one year, the effect of frozen storage

was similar for the four cultivars assayed. No major changes in the total phenolic content was

observed along with a continuous decrease in the total ellagic acid content, with losses varying

from 14 to 21%. The authors attributed the decrease in this polyphenolic compound to a possible

release of the enzyme polyphenol oxidase from the cellular wall of the fruits during storage.

22

MACRO DATA

The goal of the macro analysis presented here was to use meta-analysis techniques to go

beyond descriptive statistics and reveal inherent traits and tendencies pertaining to the nutritional

value of frozen and non frozen fruits and vegetables. More specifically, statistical analyses were

done in an attempt to evaluate variables (factors) present in the pre-freezing treatments, freezing,

and frozen storage that would explain possible differences between the frozen and non-frozen

products. Finally, through analyses of variance, statistical comparisons were made to identify

differences in the nutritional value of specific components of a variety of fruits and vegetables,

when sufficient data was available.

The data reported in the literature for the nutritional content of fruits and vegetables

includes many inherent variables, such as origin of the product, the harvesting year, storage time

and conditions, pretreatment, processing time and conditions, and method of analysis. The macro

data set was prepared by recording information about these factors from both the horizontal and

vertical searches in a spreadsheet format in a way that numerical analysis was feasible, yet

retaining enough information in each row of data that would enable the reader to understand the

content of the original paper (except for the original qualitative interpretation). The retained

information from the articles was recorded in 81 variables such as:

• Fruit or vegetable name (common or botanical)

• Variety

• Vegetable or fruit

• Vegetable/fruit form (e.g. frozen, canned, fresh, dried)

• Processing technology

• Storage time and temperature

• Wet, dry or fresh basis

• Pretreatment (blanching, etc.)

• Type of container if processed (enamel-coated, tin-plated, etc.)

• Nutrient quantities

• Geographic location

• Year published

23

• Year of comparison

• Sample size

Data Aggregation

Because of the number of variables previously mentioned, and the limited amount of information

in the literature concerning each of those variables, data aggregation was necessary in order to

facilitate the analysis and statistical inference. Several layers of aggregation were performed:

1. Nutrient types – a total of 206 different nutrient/mineral/antioxidant types measured in

the articles were combined into 25 general groups (e.g. Arabinose, Mannose, Rhamnose,

Uronic Acids, Water-Soluble Pectin, and Xylose were combined in one group called

“Soluble Fiber”).

2. Measurement units – when possible, units were converted into the ones most commonly

used in a particular group (“nutrient types” as defined in step 1 above). For example, for

vitamin C, the measurement units used by different authors were g/kg, mEq/100g,

mg/100g, mg/g, nanomoles of GAE, and µmol/g. From this list, mg/100g was the most

commonly used unit of measure (473 times), therefore measurements done in g/kg and

mg/g were converted into mg/100g by using attenuation factors of 100 and 0.01,

respectively. The rest of the measurement units were left unchanged. Afterwards, all

measurement units were classified on a dry or wet weight (fresh weight) basis.

3. A simple linear transformation was performed to convert nutrient quantities reported in

wet or fresh weight bases to those in dry weight basis, where moisture contents were

reported as well.

4. Vegetable/fruit name – over 300 different vegetable and fruit varieties were aggregated

into 105 distinct vegetable or fruit groups. For example, asparagus of different varieties

(no variety identified, Libras 10 variety, and Viking 2G) were all combined in one

“Asparagus” group. (Please note that White Asparagus comprises a distinct group.)

In the process of aggregating the data, some specific information concerning the nutrient

type, vegetable or fruit variety, and/or measurement unit was not described in the tables

24

presented in this review. To obtain such specific information, the readers should refer to the

original papers. Corresponding references are made in the footnotes of each table.

The macro data presented in Tables 3 – 7 are arranged in such a manner as to preserve the

uniform presentation of the data as much as possible. The data are presented by fruit or vegetable

form, such as fresh, frozen, canned or juiced. Fresh and frozen products are further divided into

“cooked” and “uncooked” categories. The data are presented as statistical means, with an

interval of one standard deviation around the mean, followed by the sample range and size. It

should be noted that the data points that contribute to the means, standard deviations and the

range reported in the macro dataset, may represent separate trials or averages of several trials as

different authors present their findings in different formats. In addition, the statistics are

calculated using different numbers for sample size. Therefore, any point estimates, such as the

means of even the same fruit or vegetable across their forms of fresh, frozen, canned or juiced

should be interpreted with care. A more appropriate comparison could be made by using

intervals and other sample location statistics such as the minima, maxima and medians. It is

important to consider that the variation in reported values is due to variations within a single

research paper and among different research papers. For example, variation in quantities of a

particular nutrient in a particular product are expected to be smaller when reported by just one or

a few articles as compared to quantities reported by numerous articles, ceteris paribus. Because

of this, in the presence of high variation in nutrient quantities, other location and spread statistics

are presented as well.

For some products with relatively large sample size, statistical tests are provided for

comparison of corresponding mean values of “cooked” or “uncooked” products: t-statistics and

their p-values. The 1-tailed heteroskedastic t-test statistic with unequal sample sizes is calculated

as:

25

where and are the means of the respective frozen and non-frozen product in cooked or

uncooked form,

and

with the degrees of freedom of

where, , , and are the standard deviations and sample sizes of frozen and non-

frozen products, respectively.

By definition all variables for all the products have distributions with lower bound of 0,

since the variables represent actual quantities of nutrients and therefore cannot take negative

values, and an upper bound of a real number. Assumptions concerning the shape, symmetry or

any other moment characteristics that the distributions might have are not made. For verification

purposes, the values from the data set were compared to the corresponding values provided by

USDA National Nutrient Database for Standard Reference, Nutrient Data Laboratory,

Agricultural Research Service, USDA.

26

Macro Data: Trends and Interpretation

Ascorbic Acid

Ascorbic acid is an essential part of the everyday diet and is present in leafy green

vegetables, broccoli, tomatoes, etc. Although the macro data on ascorbic acid are available on a

dry or wet (fresh) weight basis, comparisons between the two groups of data is not possible,

therefore this report presents data recorded only on a dry weight (DW) basis (data either reported

in dry weight basis or converted to dry weight basis by the authors of this review) (Table 3).

Average ascorbic acid point estimates are larger for uncooked products compared to their

cooked counterparts, as expected. Frozen uncooked broccoli and Brussels sprouts have the

highest quantities of ascorbic acid at 968.97 and 618.43 mg/100g DW, respectively. For

verification purposes, these numbers were compared to the corresponding values provided by

USDA National Nutrient database. The corresponding values (converted from wet weight to dry

weight basis by the authors of this review) for ascorbic acid for broccoli and Brussels sprouts are

722.75 and 573.09, drawn from samples of 39 and 28 trials (labeled “Number of Data Points” in

the USDA database), respectively. These values, although on the lower side, are well within the

data range in this database. From Table 3, broccoli and cauliflower have the highest ascorbic

acid quantities among fresh uncooked vegetables with 890.16 and 1038.01 mg/100g DW,

respectively. The corresponding USDA database values for these vegetables are 833.65 and

607.82, drawn from 19 and 28 trials, respectively. The relatively high value for fresh uncooked

cauliflower is possibly the result of a small number of trials (n = 4) and articles (3 articles) that

reported values for this analysis. Frozen cooked broccoli and asparagus, and fresh cooked

broccoli and cauliflower have the highest values in their corresponding categories (Table 3).

Statistical measures for frozen and fresh cooked asparagus reveal no statistical difference

(t-value = -0.1370, p-value = 0.8950) between their mean estimates of 285.52 and 291.25

mg/100g DW, respectively. Similar results were obtained when comparing uncooked frozen and

fresh green beans (t-value = 0.0547, p-value = 0.4786). Alternatively, the null hypothesis that

the mean of cooked frozen and fresh green bean values are statistically identical was rejected (t-

value = 2.2943, p-value = 0.0181), revealing that frozen cooked green beans have higher average

ascorbic acid contents than their fresh counterparts.

27

The statistical analysis failed to reject the null hypotheses that frozen and fresh cooked

and uncooked broccoli, frozen and fresh cooked green peas mean values are equal. The mean

ascorbic acid levels in cooked frozen carrots were significantly higher than the mean values for

fresh carrots (t-value = 29.49, p-value = 0.0000). On the other hand, mean ascorbic acid levels in

cooked frozen spinach are significantly lower than the mean values for frozen spinach (t-value =

-5.0466, p-value = 0.0008).

B Vitamins

The B vitamin family is another essential part of the diet. This family includes thiamin,

riboflavin, niacin, pantothenic acid, biotin and folacin, also referred to as vitamins B1, B2, B3, B5,

B7, and B9, respectively. The macro dataset presented in Table 4 contains means, standard

deviations and sample sizes for thiamin, riboflavin and niacin only, expressed in mg/100g DW.

Since the sample sizes were not sufficient for a formal statistical analysis, the data on Table 4

can only indicate general levels of vitamin B in vegetables.

The B vitamin family data came from two articles only (see the footnote to Table 4). Due

to small number of observations per product the sample data range is not reported in Table 4.

The comparison of the means in Table 4 to the USDA National Nutrient database reveal

remarkably close values, which is surprising given the extremely small sample sizes in both the

USDA and this data sets.

Based on this limited data, the highest values for thiamin were observed in asparagus,

green peas, spinach, cauliflower, and carrots, with uncooked having higher values than cooked

vegetables. This is not unexpected given the instability of thiamin in thermal processing. For

riboflavin (vitamin B2), the highest values were observed in spinach, asparagus, broccoli and

cauliflower. Once again, higher values in uncooked when compared to cooked vegetables were

observed. Asparagus, squash, spinach, broccoli, green peas and cauliflower showed the highest

contents for niacin with the tendency for higher quantities in uncooked vegetables. Potatoes, corn

and beets do not seem to have high values of vitamin B based on the data shown.

28

Table 3: Average Ascorbic Acid1 levels (mg/100g Dry Weight) in a variety of vegetables.

Frozen Fresh Canned Vegetable Uncooked Cooked Uncooked Cooked Asparagus Mean±StDev Range Count

-

285.52a±64.57 180.00 – 340.00

5

474.00

1

291.25a±60.44 201.00 – 329.00

4 -

White Asparagus Mean±StDev Range Count

-

-

48.00±31.10 21.00 – 82.00

3 -

21.87±8.86 12.80 – 30.50

3 Green Beans Mean±StDev Range Count

159.24a±48.34 22.00 – 213.00

18

138.80a±52.26 66.67 – 221.90

13

157.31a±115.64 19.80 –395.42

12

81.35b±61.26 14.60 – 176.47

9 -

Lima Beans Mean±StDev Range Count

-

38.62±3.58 33.15 – 42.78

6 -

-

-

Beets Mean±StDev Range Count

-

-

45.80

1

38.50±3.90 33.90 – 43.00

4 -

Broccoli Mean±StDev Range Count

968.97a±221.96 706.96 – 1408.00

19

625.01a±48.61 574.07 – 685.19

4

890.16a±194.92 394.91 – 1339.45

34

688.63a±237.71 425.00 – 1000.00

6 -

Brussels Sprouts Mean±StDev Range Count

618.43±135.94 522.31 – 714.55

2 -

-

-

-

Cabbage Mean±StDev Range Count

-

-

624.94±56.22 549.63 – 759.00

11

472.71±84.32 336.00 – 588.00

6 -

Carrots Mean±StDev Range Count

-

85.89a±3.78 81.76 – 89.61

5

66.58±16.75 34.70 – 100.00

15

25b.15±2.35 21.90 – 27.40

4 -

Cauliflower Mean±StDev Range Count

-

-

1038.01±174.31 872.00 – 1232.36

4

597.46±128.31 412.00 – 735.85

6 -

1 Kylen et al., 1961; Krehl and Winters, 1950; Drake et al., 1981; Martin-Belloso and Llanos-Barriobero, 2001; Eheart and Odland, 1972; Albrecht et al.,1990; Drake and Carmichael, 1986; Lane et al., 1984; Wu et al, 1992; Van Duyne et al., 1944; Barth et al., 1990.

Different superscript letters denote a significant statistical difference (p<0.10) between the means for fresh and frozen, uncooked, for each vegetable.

29

Table 3: Continued

Frozen Fresh Canned Vegetable Uncooked Cooked Uncooked Cooked Corn Mean±StDev Range Count

-

51.27±4.19 46.91 – 57.45

5

53.70±13.99 41.10 – 73.17

5

27.73±2.60 24.70 – 30.80

4 -

Eggplant Mean±StDev Range Count

-

-

79.17±11.79 70.83 – 87.50

2 -

-

Mustard Greens Mean±StDev Range Count

-

-

97.70

1

42.97±1.88 40.80 – 44.20

3 -

Green Peas Mean±StDev Range Count

-

66.77a±8.78 50.27 – 84.32

11

110.27±57.95 24.70 – 219.78

14

77.93a±48.64 17.60 – 139.42

10 -

Potatoes Mean±StDev Range Count

-

-

129.23±43.12

5

57.10±16.81

4 -

Rhubarb Mean±StDev Range Count

-

-

146.98±7.73 140.48 – 156.52

4 -

-

Savoy Cabbage Mean±StDev Range Count

-

-

862.64±152.17 719.04 – 934.24

2 -

-

Soybean Mean±StDev Range Count

-

-

82.94±16.68 63.58 – 118.52

15

58.57±0.36 58.31 – 58.82

2 -

Spinach Mean±StDev Range Count

325.52±58.79

283.95 – 367.09 2

183.77a±28.65 155.34 – 223.21

4

774.42±141.94 545.00 – 945.95

6

355.45b±75.58

268.00 – 468.47 6

-

Squash Mean±StDev Range Count

-

-

285.00

1

183.25±28.74

144.00 – 213.00 4

-

Tomatoes Mean±StDev Range Count

-

-

11.77±3.98 8.10 – 16.00

3 -

7.55±1.48 6.04 – 9.00

3

30

Table 4: Average data for B vitamins2 (mg/100g Dry Weight) in a variety of vegetables Vegetable

Form of Vegetable

Thiamin (B1)

Riboflavin B2

Niacin B3

Asparagus

Fresh Uncooked

1.58 1

2.24 1

15.50 1

Fresh Cooked

1.20±0.24 4

1.53±0.18 4

12.32±2.13 4

Green Beans

Fresh Uncooked

0.61 1

1.18 1

6.47 1

Fresh Cooked

0.56±0.07 4

0.95±0.13 4

5.28±0.78 4

Beets

Fresh Uncooked

0.28 1

0.36 1

3.00 1

Fresh Cooked

0.21±0.04 4

0.30±0.03 4

2.56±0.33 4

Broccoli

Fresh Uncooked

0.70 1

1.59 1

6.99 1

Fresh Cooked

0.56±0.07 4

1.26±0.15 4

5.23±1.49 4

Cabbage

Fresh Uncooked

0.90 (1)

0.83 (1)

3.77 (1)

Fresh Cooked

0.65±0.10 4

0.60±0.14 4

2.64±0.60 4

Carrots

Fresh Uncooked

1.10 1

0.50 1

5.42 1

Fresh Cooked

0.92±0.10 4

0.43±0.05 4

4.76±0.57 4

Cauliflower

Fresh Uncooked

1.18±0 1

1.46 1

6.79 1

Fresh Cooked

0.84±0.17 4

1.09±0.15 4

5.15±0.79 4

Corn

Fresh Uncooked

0.42 1

0.42 1

6.54 1

Fresh Cooked

0.34±0.04 4

0.32±0.08 4

4.95±1.13 4

Green Peas

Fresh Uncooked

1.25 1

0.77 1

8.24 1

Fresh Cooked

0.98±0.18 4

0.65±0.07 4

6.90±1.01 4

Potatoes

Fresh Uncooked

0.42 1

0.17 1

4.28 1

Fresh Cooked

0.34±0.03 4

0.14±0.02 4

3.30±0.47 4

Spinach

Fresh Uncooked

1.22 1

2.86 1

7.53 1

Fresh Cooked

0.87±0.19 4

2.06±0.34 4

5.18±1.54 4

Squash

Fresh Uncooked

0.85 1

0.11 1

13.30 1

Fresh Cooked

0.66±0.10 4

0.09±0.01 4

10.37±1.42 4

2 Martin-Belloso and Llanos-Barriobero, 2001; Krehl and Winters, 1950.

31

Fiber

Total, soluble, and insoluble fiber have been researched mostly in fresh fruits and

vegetables as evidenced by this review. While reviewing the literature, nine studies on total fiber

and ten studies on soluble and insoluble fiber components in fruits and vegetables were found.

Among processed products, more studies analyzed total fiber in canned vegetables and fruits

than in frozen ones; therefore there were limited data available for a formal statistical analysis.

For this reason, the data on Table 5 can only indicate general levels of total fiber in cooked and

uncooked fruits and vegetables.

Frozen raw blackberry, green beans, broccoli, cabbage, kale, and spinach showed higher

values of total fiber – 38.27, 32.46, 31.70, 32.80, 33.48 and 33.73 g/100g DW, respectively. For

fresh, uncooked fruits and vegetables, raspberry, cauliflower and spinach showed the highest

values of total fiber ranging from 33.55 to 38.05 g/100g DW. In the canned category, asparagus

and carrots had the highest values of fiber, 32.23 and 31.25, respectively. The total dietary fiber

mean values, standard deviations, sample data ranges and sample sizes are reported in Table 5.

Due to very limited sample size, hypothesis testing with t statistic was not performed, as

the power of the test declines with the sample size. Instead, fiber content means and intervals

were relied upon for comparisons when frozen and non-frozen values were available. The mean

level of dietary fiber for frozen uncooked broccoli, cabbage, carrots, green peas and spinach

compared favorably to their fresh counterparts (Table 5). In contrast, fresh uncooked cauliflower

and potatoes have higher mean levels of fiber than their frozen counterparts. Once again these

values are similar to corresponding values in frozen and fresh uncooked products obtained from

the USDA National Nutrient database (converted from wet weight basis to dry weight basis

when necessary).

32

Table 5: Average data for Total Fiber3 (g/100g Dry Weight) in a variety of fruits and vegetables Fruit / Frozen Fresh Canned Vegetable Uncooked Cooked Uncooked Cooked Apple Mean±StDev Range Count

-

-

13.67±1.37 11.76 – 15.03

5 -

-

Applesauce Mean±StDev Range Count

-

-

-

-

11.97±1.44 10.43 – 13.29

3 Apricot Mean±StDev Range Count

-

-

13.72±0.63 13.27 – 14.16

2 -

-

Asparagus Mean±StDev Range Count

-

-

-

-

32.23

1 White Asparagus Mean±StDev Range Count

-

-

-

-

10.44

1 Banana Mean±StDev Range Count

-

-

7.61±0.24 7.35 – 7.83

3 -

-

Green Beans Mean±StDev Range Count

32.46±1.68 31.27 – 33.65

2 -

-

-

-

Yellow Beans Mean±StDev Range Count

-

-

28.33±0.79 27.78 – 28.89

2

28.57±2.89 26.53 – 30.61

2

29.33±1.89 28.00 – 30.67

2 Beets Mean±StDev Range Count

-

-

-

332.22±80.14

275.56 – 388.89 2

24.57±0.26

24.27 – 24.72 3

Blackberry Mean±StDev Range Count

38.27±1.19 37.43 – 39.11

2 -

-

-

-

Blueberry Mean±StDev Range Count

-

-

17.68±0.05 17.64 – 17.71

2 -

-

3 Marlett and Vollendorf, 1994; Anderson and Bridges, 1988; Mongeau and Brassard, 1989; Martin-Belloso and Llanos-Barriobero, 2001; Marlett and Vollendorf, 1993; Kmiecik et al., 2001; Khanum et al., 2000; Puupponen-Pimiä et al. 2003.

33

Table 5: Continued

Fruit / Frozen Fresh Canned Vegetable Uncooked Cooked Uncooked Cooked Broccoli Mean±StDev Range Count

31.70±1.84 30.40 – 33.00

2 -

29.15±3.10 26.95 – 31.34

2 -

-

Brussels Sprouts Mean±StDev Range Count

26.94

1 -

-

-

-

Butternut Squash Mean±StDev Range Count

-

-

-

18.60±5.26 14.88 – 22.31

2 -

Cabbage Mean±StDev Range Count

32.80

1 -

25.91±5.86 20.66 – 39.60

8

25.00±0.00 25.00 – 25.00

2 -

Cantaloupe Mean±StDev Range Count

-

-

7.33±0.06 7.29 – 7.37

2 -

-

Carrots Mean±StDev Range Count

28.24±2.96 24.20 – 31.70

5 -

25.87±5.16 23.36 – 39.50

9

31.36±3.21 29.09 – 33.64

2

31.25±0.98 30.56 - 31.94

2 Cauliflower Mean±StDev Range Count

30.00±4.67 26.70 – 33.30

2 -

38.05±11.10 30.20 – 45.90

2 -

-

Celery Mean±StDev Range Count

-

-

27.46±2.61 25.61 – 29.30

2 -

-

Cherry Mean±StDev Range Count

-

-

7.25±1.16 6.44 – 8.01

2 -

-

Corn Mean±StDev Range Count

-

-

-

5.33±0.78 4.78 – 5.88

2

7.64±1.65 6.18 – 9.43

3 Cranberry Mean±StDev Range Count

-

-

-

-

3.17±0.54 2.79 – 3.55

2 Cucumbers Mean±StDev Range Count

-

-

18.19±0.20 18.06 – 18.33

2 -

-

34

Table 5: Continued

Fruit / Frozen Fresh Canned Vegetable Uncooked Cooked Uncooked Cooked Grapefruit Mean±StDev Range Count

-

-

13.22±1.50

11.80 – 14.79 3

-

-

Grape Mean±StDev Range Count

-

-

4.91±0.83 4.19 – 6.10

4 -

-

Grass peas Mean±StDev Range Count

-

-

25.14±30.70 9.30 – 80.00

5

11.52±2.34 8.50 – 14.10

5

13.05±3.34 8.50 – 16.50

10 Green Peas Mean±StDev Range Count

24.65±1.39 22.90 – 26.30

4 -

23.08±2.48 20.00 – 25.90

4 -

-

Green Peppers Mean±StDev Range Count

-

-

27.90±0.72

27.39 – 28.41 2

-

-

Kale Mean±StDev Range Count

33.48

1 -

-

-

-

Lettuce Mean±StDev Range Count

-

-

25.19±4.04

21.02 – 29.09 3

-

-

Onion Mean±StDev Range Count

-

4.13±0.43 3.83 – 4.44

2

14.23±0.58 13.51 – 14.80

5

17.14±0.88 15.96 – 18.09

4 -

Orange Mean±StDev Range Count

-

-

11.91±1.11

10.20 – 13.68 7

-

1.55±0.44 1.24 – 1.86

2 Peach Mean±StDev Range Count

-

-

12.98±1.39 10.48 – 14.29

6 -

12.38±5.56 8.86 – 18.80

3 Pear Mean±StDev Range Count

-

-

11.82±0.43 11.51 – 12.12

2 -

32.18

1 Pineapple Mean±StDev Range Count

-

-

-

-

7.13±2.09 5.80 – 9.54

3

35

Table 5: Continued

Fruit / Frozen Fresh Canned Vegetable Uncooked Cooked Uncooked Cooked Plum Mean±StDev Range Count

-

-

11.08±1.67 9.47 – 13.25

4 -

12.42±9.02 6.67 – 22.81

3 Potatoes Mean±StDev Range Count

4.90±0.57 4.50 – 5.30

2 -

8.05±3.63

4.70 – 12.50 4

7.87±1.12

6.00 – 10.00 14

-

Raspberry Mean±StDev Range Count

-

-

34.55±1.72

33.33 – 35.77 2

-

-

Red Lettuce Mean±StDev Range Count

-

-

23.58±1.33 22.64 – 24.53

2 -

-

Spinach Mean±StDev Range Count

33.73±7.04

28.75 – 38.70 2

-

33.55±13.57 21.36 – 51.70

4

27.71±5.11

24.10 – 31.33 2

-

Squash Mean±StDev Range Count

19.79

1

-

-

20.71±3.28

17.02 – 24.44 4

-

Strawberry Mean±StDev Range Count

11.43±6.28 5.88 – 17.76

4 -

-

-

-

Tomatoes Mean±StDev Range Count

-

-

15.86±2.88 13.13 – 21.00

6 -

9.64

(1)

36

Calcium

Despite the fact that several minerals such as calcium, iron, magnesium, phosphorus, and

sodium have been addressed by studies reviewed by this project, calcium was the only one where

enough observations were found to be included in the dataset. The included articles had their

calcium analyses mostly done on fresh fruits and vegetables. Calcium is a very important part of

the diet and according to the Continuing Survey of Food Intakes by Individuals (CSFII) and

National Health and Examination Survey, National Center for Health Statistics (NHANES),

USDA is chronically underconsumed. This could be a reason why so many reports in the

literature address this mineral.

The data in Table 6 indicate that fresh uncooked broccoli, spinach, green beans, squash

and cabbage are sources of non-dairy calcium with 1364, 1140, 725, 720 and 622 mg/100g D W,

respectively. From the data reported in Table 6, higher average levels of calcium were observed

in uncooked when compared to cooked vegetables. It should be noted that these data are merely

one point estimates from a whole distribution, and as such may or may not be meaningful

approximations to distributional traits, such as the mean location. Similar shortcomings, but to a

lesser degree, affects the mean calcium values of cooked fresh products. In general the values for

both cooked and uncooked products do not compare well to the corresponding converted values

obtained from the USDA National Nutrient database.

37

Table 6: Average data for Calcium4 (mg/100g Dry Weight) in a variety of vegetables

Vegetable Frozen Fresh Uncooked Cooked Uncooked Cooked Asparagus

-

-

315 1

296±15.56 4

Green Beans

-

-

725 1

684.50±36.95 4

Beets

-

-

268 1

247±17.45 4

Broccoli

-

-

1364 1

1177.25±61.08 4

Cabbage

-

-

622 1

551±43.95 4

Carrot

-

-

350 1

310.25±21.19 4

Cauliflower

-

-

336 1

293.50±13.30 4

Corn

-

-

32.10 1

27.73±1.69 4

Green Peas

-

-

99.60 1

86.18±6.25 4

Potatoes

-

-

61.60 1

46.35±8.63 4

Spinach

-

-

1140 1

930.75±70.84 4

Squash

-

-

720 1

547±98.44 4

4 Martin-Belloso and Llanos-Barriobero, 2001; Krehl and Winters, 1950.

38

Carotenoids

Carotenoids are micronutrients found primarily in fruits and vegetables such as carrots.

Carotenoids have been extensively addressed in the literature and the alpha and beta carotene

contents for a variety of vegetables (carrots, corn, hot peppers and spinach) are shown in Table 7.

Based on the data reported in the table, corn and carrots have the highest frozen uncooked beta

carotene levels, with 9.53 and 6.75 mg/100g fresh weight, respectively. Based on the corn data

in Table 7, there is limited evidence that frozen corn has higher levels of alpha and beta carotene

than canned corn.

The corresponding values for the USDA National Nutrient Database for frozen uncooked

and fresh cooked carrots are 7.05 and 3.78 mg/100g Fresh Weight, respectively, which compare

well with the values from this data set: 6.75 and 4.75 mg/100g Fresh Weight, respectively.

However, corn and spinach do not compare closely with the corresponding values from the

USDA National Nutrient Database.

39

Table 7: Average data for Alpha and Beta Carotene (mg/100g Fresh Weight) in a variety of

vegetables

Vegetable

Form of Vegetable

Beta carotene5

Alpha carotene6

Carrots

Frozen Uncooked

6.75±2.05 2

-

Frozen Cooked

-

-

Fresh Uncooked

-

-

Fresh Cooked

-

4.75±1.48 2

Canned

-

-

Corn

Frozen Uncooked

9.53±10.12 2

3.52±4.65 2

Frozen Cooked

-

-

Fresh Uncooked

8.26±10.51 2

5.87±8.24 2

Fresh Cooked

-

-

Canned

6.17±7.76 2

2.23±3.08 2

Spinach

Frozen Uncooked

2.45±1.06 2

-

Frozen Cooked

-

-

Fresh Uncooked

-

-

Fresh Cooked

-

-

Canned

-

-

5 Scott and Eldridge, 2004; Borchgrevnik and Charley, 1966; Sweeney and Marsh, 1971; Mejia et al., 1988.

6 Zhang and Hamauzu, 2004; Scott and Eldridge, 2004; Padula and Rodriguez-Amaya,1986; Wu et al., 1992; Borchgrevnik and Charley, 1966; Sweeney and Marsh, 1971; Mejia et al., 1988.

40

CONCLUSIONS

After extensively reviewing the literature on the effects of freezing and frozen storage of

fruits and vegetables, some points of concern were raised. The amount of data that directly

compares fresh and frozen fruits and vegetables is very limited, with most of the data dating back

at least 20-30 years when some of the methodology for determination of vitamins and other

nutritional compounds was also limited. Also, many of the articles make comparisons of specific

compounds of fruits and vegetables using a wet weight basis without giving the reader an insight

on the moisture content of the products in discussion. Some papers even mention that the

differences found could be caused by loss of water in one of the processing steps. Simply by

providing the moisture content of the products or reporting the results on a dry weight basis

would solve much of the problem and even allow for better cross-comparison of data among

articles.

Several articles compare the nutritional value of fresh and frozen fruits and vegetables

available at retail stores, without considering the source of those products (harvesting location,

harvesting year, maturity, and method of processing). Although these comparisons are valid to

indicate the availability of nutrients and phytochemicals offered by the products surveyed it does

not truly represent the effects of freezing and frozen storage. Variation on the chemical and

nutritional composition of cauliflower was evaluated by Nilsson (1980) based on soil type,

nitrogen and irrigation. The results showed that all variables affected the chemical composition

of cauliflower, with the effects of nitrogen and irrigation varying from one soil to another.

Morrison (1975) reported that the vitamin C content of green beans may change with maturity

and also the variability of this compound within one variety when multiple samples were taken

before and after freezing.

Another area within the body of literature that needs further exploration is the effects of

the freezing process and frozen storage on processed fruits and vegetables in the form of juice,

concentrate, or pulp. This is especially important in a global economy because of the volume of

fruit products (pulp and concentrates) that are exported and imported around the world. Most

originate in tropical areas and are consumed months later in areas where the cultivation of these

plants is less favorable or impossible. These products are commercially available directly to

consumers at retail stores, but the knowledge about their true nutritional value and the

41

bioavailability of important phytochemicals becomes even more essential for the food industry

that uses these products as ingredients in a variety of other processed foods. Evaluating how the

nutritional value of these products may change during frozen storage and transport from supplier

to end user (consumer or processor) is essential to determine if improvements in the system are

necessary.

Regarding the effects of storage, some authors have indicated the lack of research

covering the -3 to -10oC range, which is very detrimental and does frequently occur in real-world

transport and retail storage along the frozen chain. Shelf-life modeling under temperature

fluctuations would help address these concerns in a reliable way. The establishment of kinetic

equations that would cover the relevant range of temperature and be validated under dynamic,

non-isothermal conditions is essential to the assessment of the nutritional value of a product

based on its temperature history (Giannakourou and Taoukis, 2003).

The goal of compiling the macro data set is to determine possible causal relationships

between certain nutritional levels in fruits and vegetables and factors contributing to those levels

and draw statistical inferences. From those factors, the state of the product being frozen or non-

frozen is the central objective of this review. The macro data set also helps to create

distributions of nutritional contents, such as vitamins B and C, alpha and beta carotenes, calcium

and fiber, for some key fruits and vegetables.

Many factors contribute to the variability of the nutritional content of fruits and

vegetables reported in the literature. These factors, which include but are not limited to the

complexity of the subject matter, the analytical method used even within a certain class, and

purely statistical data-related problems (e.g. missing observations, influential data points,

insufficient number of observations), contributed to the infeasibility of regression analysis of the

data. Preparation, storage times, and methods are examples with extremely wide distribution,

which increases the dispersion and reduces the sample sizes so severely that it is practically

impossible to perform regression analyses on the data. These factors limited the ability to draw

regression inferences on the nutritional contents of fruits and vegetables, and resulted only in the

performance of distributional analyses of means and dispersions of the data.

42

When possible, the means in the dataset were verified by comparing them to those

reported in other studies or by government agencies. Verifying the trends is challenging as there

are few, if any, sources performing similar analyses as this review. Because of the variability

previously discussed, even if such contemporary data was available, it may not justify direct

comparisons. For example, comparing the statistical average of some data points found in the

last 80 years or so to an average of several trials reported in any single study, or even to an

average by several studies from a different time span may not be appropriate. In summary, the

results of the macro data analysis present statistical means and dispersions of findings in the

literature, without explaining the factors causing the variations in those means.

In conclusion, the frozen foods industry is a multibillion dollar industry that provides

safe, wholesome fruits and vegetables to consumers that overall, maintain much of their

nutritional quality. Today an increasing demand for frozen foods already exists and further

expansion of the industry is primarily dependent on the ability of food processors to develop

higher quality in both process techniques and products. Therefore, improvements can only be

achieved by focusing research on new market trends and investigating the poorly understood

areas discussed here that influence the quality of frozen fruits and vegetables. Studies on the

variable effects of storage conditions, a standardization of analytical techniques, and

investigations of the nutritional content of new or exotic fruits and vegetables are all areas of

future research that will help improve and drive the marketability of frozen produce.

43

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FLORES R. [2010] NUTRITIONAL COMPARISON OF FROZEN AND NON‐FROZEN FRUITS AND VEGETABLES LITERATURE REVIEW.pdf